1. Field of the Invention
The present invention relates to a yellow pigment comprising an asymmetric quinolonoquinolone, methods of preparing this yellow pigment, and inkjet ink compositions comprising them.
2. Description of the Related Art
An inkjet ink composition generally consists of a vehicle, which functions as a carrier, and a colorant such as a dye or pigment. Additives and/or cosolvents can also be incorporated in order to adjust the inkjet ink to attain the desired overall performance properties.
Inkjet ink compositions comprising a yellow pigment has been an area of particular focus for inkjet ink manufacturers. There has been a need in the industry for an inkjet ink composition comprising a yellow pigment having excellent lightfastness and the proper balance of color strength and hue, along with good overall dispersion stability. Various classes of yellow pigments have been prepared, each with varying degrees of lightfastness and color. For example, U.S. Pat. No. 3,334,102 describes the preparation of quinolonoquinolones, which are described as having good lightfastness. Various substituted quinolonoquinolones have also been prepared. For example, JP 11-130972 and 10-017783 describe the preparation of halogenated quinolonoquinolones.
In general, pigments alone, including yellow pigments, are not readily dispersible in liquid vehicles. A variety of techniques have been developed which can provide stable pigment dispersions that can be used in inkjet printing. For example, dispersants can be added to the pigment to improve its dispersibility in a particular medium. Examples of dispersants include water-soluble polymers and surfactants. Typically, these polymeric dispersants have a molecular weight less than 20,000 in order to maintain solubility and therefore pigment stability. Yellow pigment dispersions have also been prepared using this technique. For example, JP 10-130554 describes inkjet ink compositions comprising substituted quinolonoquinolones which further comprise a rosin, resin, surfactant, or dispersant.
The surface of pigments contain a variety of different functional groups, and the types of groups present depend on the specific class of pigment. Several methods have been developed for grafting materials and, in particular, polymers to the surface of these pigments. For example, it has been shown that polymers can be attached to carbon blacks containing surface groups such as phenols and carboxyl groups. However, methods which rely on the inherent functionality of a pigment's surface cannot be applied generally because not all pigments have the same specific functional groups.
Methods for the preparation of modified pigment products, including modified yellow pigments, have also been developed. These methods can be used to produce pigments with a variety of different attached functional groups. For example, U.S. Pat. No. 5,851,280 discloses methods for the attachment of organic groups onto pigments including, for example, attachment via a diazonium reaction wherein the organic group is part of the diazonium salt. Other methods to prepare modified pigments have also been described, including PCT Publication No. WO 01/51566, which discloses methods of making a modified pigment by reacting a first chemical group and a second chemical group to form a pigment having attached a third chemical group. Ink compositions, including inkjet inks, containing these pigments are also described.
While these methods provide modified pigments, including modified yellow pigments, having attached groups, there remains a need in the industry for an inkjet ink composition comprising a yellow pigment having excellent lightfastness, the proper balance of color strength, and/or hue along with good dispersion stability.